Purpose is to limit the uninstallation of modules without being clearly
notified of it. We therefore decided to remove those options from settings
to prevent users from uninstalling it.

Description of sale_timesheet features and options are now all moved to
sale_timesheet. A Billing section should only be visible if sales installed.
We therefore move Billing section from hr_timesheet to sale_timesheet. A
priority is used to ensure sequence of various settings related to billing
and timesheet.

This commit is related to task ID 1841221.